Method and network node for uplink beam management

ABSTRACT

A method for beam management, which method is performed by a network node. The method provides for using a first receive, RX, beam to receive a first signal transmitted by a user equipment, UE. The method then provides for obtaining, based on the first signal received using the first RX beam, a first received signal power value, P1. The method then provides for using a second RX beam to receive the first signal or another signal transmitted by the UE. The method then provides for obtaining, based on the signal received using the second RX beam, a second received signal power value, P2. The method then provides for determining whether P2 exceeds P1 by at least a threshold. The method then provides for determining whether to initiate a beam sweep based on whether or not P2 exceeds P1 by at least the threshold.

TECHNICAL FIELD

Disclosed are embodiments related to beam management.

BACKGROUND

1. Beam Management

Narrow beam transmission and reception schemes are needed at higherfrequencies to compensate for high propagation loss. A suitabletransmission and reception point (TRP) transmit (TX) beam for each UE isexpected to be discovered and monitored by the network (e.g., a basestation) using measurements on downlink reference signals (RSs) used forbeam management. Such downlink reference signals include Channel StateInformation RS (CSI-RS) and synchronization signal block (SSB). Beammanagement RSs can be transmitted periodically, semi-persistently, oraperiodically (event triggered), and they can be either shared betweenmultiple UEs or be UE-specific. The SSB are transmitted periodically andare shared for all UEs. In order to find a suitable TRP TX beam, the TRPtransmits CSI-RS/SSB using different TRP TX beams, and the UE performsreference signal received power (RSRP) measurements on the receivedreference signals and reports back the N best TRP TX beams and theircorresponding RSRP values (where N can be configured by the network).

Typically, a base station makes use of three different beam managementprocedures. These three procedure are knows as: the P1 procedure, the P2procedure, and the P3 procedure, and are illustrated in FIGS. 1A, 1B,and 1C, respectively. The P1, P2, and P3 procedures are also known asthe P1 beam sweep, P2 beam sweep, and P3 beam sweep, respectively.

In the P1 procedure shown in FIG. 1A, a base station 102 uses TX beamshaving large beamwidths. Beam reference signals transmitted using the TXbeams are transmitted periodically and are shared between multiple UEs(including UE 104). Examples of the periodic beam reference signals areperiodic CSI-RS and SSB. After UE 104 receives the reference signals, UE104 may report to base station 102 the N best TRP TX beams and theircorresponding RSPR values. The beam reporting from UE 104 to basestation 102 can be performed in a periodic manner, a semi-persistentmanner, or in aperiodic manner. The P1 procedure may be used to find acoarse direction of a UE 104 with respect to base station 102.

After determining the coarse direction of UE 104, in the P2 procedureshown in FIG. 1B, base station 102 uses narrower TRP TX beams coveringthe area corresponding to the TRP TX beam selected as a result ofperforming the P1 procedure. In the P2 procedure, base station 102 maytransmit reference signals in aperiodic or semi-persist manner. The P2procedure may be performed more frequently than the P1 procedure totrack UE 104's movements or changes in the radio environment. The P2procedure may be used to select a suitable narrow TRP TX beam for use incommunicating with UE 104.

More specifically, during the P2 beam sweep, UE 104 measures RSRP foreach of the beams in the set of TRP beams 103 (using a fixed UE RX beam101) and sending back to the base station 102 the CSI-RS resourceindex(s) (CRI(s)) corresponding to the highest RSRP(s), where each CRIcorresponds to one of the TRP TX beams 103. During such P2 beam sweep itis expected that UE 104 will apply a wide beam 103 (a.k.a., anon-directional beam or omni-directional beam) (e.g. the widest beamthat the UE is able to generate) so that as many propagation paths aspossible between the base station 102 and the UE 104 are captured by theP2 beam sweep.

The P3 procedure is a procedure that enables UE 104 to select a “best”UE receive (RX) beam. For example, after finding a suitable narrow TRPTX beam as a result of performing a P2 beam sweep, in the P3 procedureshown in FIG. 1C, base station 102 transmits a burst of referencesignals using one narrow beam 107 (e.g., the narrow TRP TX beam selectedas a result of the P2 procedure) in aperiodic or semi-persistent manner.The UE 104 uses different receiving (RX) beams to receive signal(s) frombase station 102 to find a suitable RX beam at UE 104. That is, UE 104can sweep through different UE RX directional beams 105, performmeasurements on the CSI-RS and select a preferred UE RX directional beam(e.g., UE RX beam 114). How the UE determine the candidate UE RX beamsis up to UE implementation. The P3 procedure may be performed frequentlyto compensate for blocking and/or UE rotation.

Wide beams may be used in the P1 procedure described above to find acoarse direction of UE 104 with respect to base station 102. Narrowbeams may be used in the P2 procedure to find a narrow TX beam that issuitable for data transmission to UE 104.

One way of selecting narrow beams in the P2 procedure is (1) determiningwhich of the wide beams used in the P1 procedure performs the best interms of RSRP values and (2) selecting narrow beams that are confinedwithin the angular coverage of the determined wide beam. For example, inthe exemplary P1 procedure shown in FIG. 1A, wide beam 109 was the bestwide beam. Thus, in P2 procedure shown in FIG. 1B, the narrow beamsconfined within angular coverage of the wide beam 109 are selected.

2. Antenna Architectures

There are three different implementations of beamforming at a TRP—analogbeamforming, digital beamforming, and hybrid beamforming. Digitalbeamforming is the most flexible solution among the three but costs themost due to a large number of required radios and baseband chains.Analog beamforming is cheaper to manufacture as compared to the digitalbeamforming due to a reduced number of radios and baseband chains.Analog beamforming is the least flexible solution among the three, butis cheaper to implement due to reduced number of radio and basebandchains. Another drawback of the analog beamforming is that a TRP canonly transmit or receive in one beam at a time (assuming one panel, andthe same beam for both polarizations, which typically is the case inorder to counteract dropped signal strength due to polarizationmis-matching). Hybrid beamforming is a compromise between the analogbeamforming and digital beamforming. One type of beamforming antennaarchitecture that has been agreed to study in 3GPP for the NR accesstechnology is the concept of antenna panels, both at the TRP and at theUE. A panel is an antenna array of single-polarized or dual-polarizedantenna elements with typically one transmit/receive unit (TXRU) perpolarization. An analog distribution network with phase shifters is usedto steer the beam of each panel. Multiple panels can be stacked next toeach other and digital beamforming can be performed across the panels.FIG. 2 illustrates an example with two panels where each panel isconnected to one TXRU per polarization.

3. Uplink (UL) Beam Management

Some UEs have analog beamformers without beam correspondence;consequently, downlink/uplink reciprocity cannot be used to determinethe beams for these beamformers. For such UEs, the UE beam used foruplink (UL) cannot be derived from beam management procedures based ondownlink (DL) reference signals as described above. To handle such UEs,UL beam management has been included in the NR standard specificationfor release 15. The main difference between DL beam management and ULbeam management is that UL beam management utilizes UL reference signalsinstead of DL references signals. The UL reference signals that havebeen agreed to be used for UL beam management is sounding referencesignals (SRS). Two UL beam management procedures are supported in NR; U2and U3, which are schematically illustrated in FIGS. 3A and 3B. The U2procedure (a.k.a., U2 beam sweep), illustrated in FIG. 3A, is performedby transmitting a burst of SRS resources in one UE TX beam 310 andletting the base station 102 evaluate different TRP RX beams 312 a, 312b, 312 c, and 312 d. The U3 procedure, illustrated in FIG. 3B, lets theUE 104 evaluate a suitable UE TX beam by transmitting different SRSresources in different UE TX beams 314 a, 314 b, 314 c, and 314 d, whilebase station 102 receives the SRS resources using a single TRP TX beam316.

4. SRS Transmission Setting

How the SRS transmission should be performed by UE 104 is defined in aSRS-Config information element (IE), and is signaled to the UE 104 fromthe TRP with RRC signaling. As shown in Table 1 below, the SRS-Config 1Econtains a list of SRS-Resources (the list constitutes a “pool” ofresources). Each SRS resource contains information of the physicalmapping of the reference signal on the time-frequency grid, time-domaininformation, and sequence IDs. The SRS-Config also contains a list ofSRS resource sets, which contains a list of SRS resources and anassociated Downlink Control Information (DCI) trigger state. Thus, whena certain DCI state is triggered, it indicates that the SRS resources inthe associated set shall be transmitted by the UE.

Each SRS resource set can be associated with one usage, including, forexample, beamManagement, codebook, nonCodebook, antennaSwitching.

SRS resources with usage ‘codebook’ are used to sound the different UEantennas and let the base station 102 determine suitable precoders, rankand modulation, and coding scheme (MCS) for coming UL transmission. Howeach SRS port is mapped to each UE antenna is up to UE implementation,but it is expected that one SRS port will be transmitted per UE antenna.For example, the SRS port to antenna port mapping can be an identitymatrix.

SRS resources with usage ‘nonCodebook’ is used to sound differentpotential precoders by the UE 104. The UE 104 determines a set ofcandidate precoders based on reciprocity and transmits one SRS resourceper candidate precoder. The base station 102 can then select whichprecoders the UE 104 should use for physical uplink shared channel(PUSCH) transmissions. One UL layer can be transmitted per indicatedcandidate precoder. How the UE 104 maps the SRS resources to the antennaports is up to UE implementation and depends on the channelcharacteristics.

SRS resources with usage ‘antennaSwitching’ are used to sound thechannel in UL so that the base station 102 uses reciprocity to determinesuitable DL precoders. If the UE 104 has the same number of TX and RXchains, the UE 104 shall transmit one SRS port per UE antenna. UEimplementation can select which SRS port is transmitted from whichantenna.

SRS resources with usage ‘beamManagement’ are only applicable for higherfrequencies (FR2) and are used to find a suitable beam at the UE 104, bytransmitting different SRS resources in different UE TX beams. Arepetition factor up to 4 can be defined per SRS resources, which allowsthe base station 102 to evaluate up to four different TRP RX beams. TheSRS resource set with a repetition factor can be triggered multipletimes in case the base station 102 would like to evaluate more than 4TRP RX beams.

How SRS transmissions are configured and triggered for NR can be foundbelow in Table 1, which is taken from the NR specification 3GPP TS38.331 [Version 15.7.0]:

TABLE 1 2.1.1.1 SRS-Config The SRS-Config Information Element (IE) isused to configure sounding reference signal transmissions. Theconfiguration defines a list of SRS-Resources and a list ofSRS-ResourceSets. Each resource set defines a set of SRS-Resources. Thenetwork triggers the transmission of the set of SRS-Resources using aconfigured aperiodicSRS-ResourceTrigger (that is carried in physicallayer downlink control information, ‘L1 DCI’).  SRS-Config informationelement -- ASN1START -- TAG-SRS-CONFIG-START SRS-Config ::=  SEQUENCE { srs-ResourceSetToReleaseList SEQUENCE(SIZE(1..maxNrofSRS-ResourceSets)) OF SRS-ResourceSetId OptIONAL,  --Need N  srs-ResourceSetToAddModList SEQUENCE(SIZE(1..maxNrofSRS-ResourceSets)) OF SRS-ResourceSet OptIONAL,  -- NeedN  srs-ResourceToReleaseList SEQUENCE (SIZE(1..maxNrofSRS-Resources)) OFSRS-ResourceId OptIONAL,  -- Need N  srs-ResourceToAddModList SEQUENCE(SIZE(1..maxNrofSRS-Resources)) OF SRS- Resource OptIONAL, -- Need N tpc-Accumulation   ENUMERATED {disabled} OptIONAL, -- Need S  ... }SRS-ResourceSet ::= SEQUENCE {  srs-ResourceSetId  SRS-ResourceSetId, srs-ResourceIdList  SEQUENCE (SIZE(1..maxNrofSRS-ResourcesPerSet)) OFSRS-ResourceId  OPTIONAL,   -- Cond Setup  resourceType  CHOICE {  aperiodic SEQUENCE {    aperiodicSRS-ResourceTrigger INTEGER(1..maxNrofSRS-TriggerStates-1),    csi-RS  NZP-CSI-RS-ResourceIdOptIONAL, -- Cond NonCodebook    slotOffset  INTEGER (1..32)OptIONAL, -- Need S    ...,    [[   aperiodicSRS-ResourceTriggerList-v1530 SEQUENCE (SIZE(1..maxNrofSRS-TriggerStates-2)) OF INTEGER (1..maxNrofSRS-TriggerStates-1) OptIONAL --Need M    ]]   },   semi-persistent    SEQUENCE {    associatedCSI-RSNZP-CSI-RS-ResourceId OptIONAL, -- Cond NonCodebook    ...   },  periodic SEQUENCE {    associatedCSI-RS NZP-CSI-RS-ResourceIdOptIONAL, -- Cond NonCodebook    ...   }  },  usage  ENUMERATED{beamManagement, codebook, nonCodebook, antennaSwitching},  alpha  AlphaOptIONAL, -- Need S  p0   INTEGER (−202..24)  OptIONAL, -- Cond Setup pathlossReferenceRS  CHOICE {   ssb-Index SSB-Index,   csi-RS-IndexNZP-CSI-RS-ResourceId  }  OptIONAL, -- Need M srs-PowerControlAdjustmentStates ENUMERATED { sameAsFci2,separateClosedLoop} OptIONAL, -- Need S  ... } SRS-ResourceSetId ::=  INTEGER (0..maxNrofSRS-ResourceSets-1) SRS-Resource ::=  SEQUENCE { srs-ResourceId   SRS-ResourceId,  nrofSRS-Ports   ENUMERATED {port1,ports2, ports4},  ptrs-PortIndex   ENUMERATED {n0, n1} OptIONAL, -- NeedR  transmissionComb   CHOICE {   n2  SEQUENCE {    combOffset-n2 INTEGER(0..1),    cyclicShift-n2 INTEGER (0..7)   },   n4 SEQUENCE {   combOffset-n4 INTEGER (0..3),    cyclicShift-n4 INTEGER (0..11)   } },  resourceMapping   SEQUENCE {   startPosition    INTEGER (0..5),  nrofSymbols ENUMERATED {n1, n2, n4},   repetitionFactor    ENUMERATED{n1, n2, n4}  },  freqDomainPosition  INTEGER (0..67),  freqDomainShift  INTEGER (0..268),  freqHopping  SEQUENCE {   c-SRS INTEGER (0..63),  b-SRS INTEGER (0..3),   b-hop INTEGER (0..3)  }, groupOrSequenceHopping ENUMERATED { neither, groupHopping,sequenceHopping },  resourceType  CHOICE {   aperiodic SEQUENCE {    ...  },   semi-persistent  SEQUENCE {    periodicityAndOffset-spSRS-PeriodicityAndOffset,    ...   },   periodic SEQUENCE {   periodicityAndOffset-p SRS-PeriodicityAndOffset,    ...   }  }, sequenceId  INTEGER (0..1023),  spatialRelationInfo SRS-SpatialRelationInfo OptIONAL, -- Need R  ... }SRS-SpatialRelationInfo ::= SEQUENCE {  servingCellId  ServCellIndexOptIONAL, -- Need S  referenceSignal  CHOICE {  ssb-Index  SSB-Index, csi-RS-Index NZP-CSI-RS-ResourceId,   srs  SEQUENCE {    resourceIdSRS-ResourceId,    uplinkBWP BWP-Id   }  } } SRS-ResourceId ::= INTEGER(0..maxNrofSRS-Resources-1) SRS-PeriodicityAndOffset ::= CHOICE {  sl1NULL,  sl2 INTEGER(0..1),  sl4 INTEGER(0..3),  sl5 INTEGER(0..4),  sl8INTEGER(0..7),  sl10 INTEGER(0..9),  sl16 INTEGER(0..15),  sl20INTEGER(0..19),  sl32 INTEGER(0..31),  sl40 INTEGER(0..39),  sl64INTEGER(0..63),  sl80 INTEGER(0..79),  sl160 INTEGER(0..159),  sl320INTEGER(0..319),  sl640 INTEGER(0..639),  sl1280 INTEGER(0..1279), sl2560 INTEGER(0..2559) } -- TAG-SRS-CONFIG-STOP -- ASN1STOP

SUMMARY

Certain challenges exist due to the fact that many user equipments (UEs)(e.g., cars, drones, smart phones, sensors, and other network-accessiblecommunication devices) are simultaneously connected to the Internet viaa base station. For base stations equipped with analog beamforming, eachbase station panel can only receive with one beam at a given time (hencein case a base station has two panels, the base station can receive withtwo beams, one per panel). An UL beam management sweep will thereforerequire exceptional overhead in order to account for the increasingnumber of UEs that are able to access the Internet via the base station.Since U2 and U3 beam sweeps are typically aperiodic, and not sharedbetween multiple UEs, the overhead of beam management is expected togrow linearly with the increasing number of UEs in the cell. This willlead to an overhead cost that severely reduces the performance of thenetwork, both with respect to capacity and latency. There is, therefore,a need to reduce the amount of overhead for UL beam managementprocedures.

In one embodiment, this reduction in overhead is achieved by having abase station trigger a UE to perform a single SRS resource transmission,while the base station receives the transmission using a wide TRP RXbeam on a first TRP panel and a narrow TRP RX beam on a second TRP panel(e.g., the narrow beam is the currently-known best TRP RX beam, whichhas been found previously using for example an extensive beam managementprocedure). The base station then compares the difference in receivedpower between the narrow beam and the wide beam (e.g.,diff=RSRP_narrow_beam−RSRP_wide_beam). If “diff” is smaller than acertain threshold (and with a proper value of the threshold), there is alarge chance that another narrow TRP RX beam is better than the currentbest narrow TRP RX beam, and the base station can then decide toinitiate a U2 beam sweep. For example, initiating a U2 beam sweepcomprises triggering an SRS resource set with repetition factor=N, whereN is, for example, 4 or more (the SRS resource set could be triggeredmultiple times in case more than N TRP beams need to be evaluated).

In one embodiment, the TRP uses received data instead of a received SRSto determine the difference in RSRP between the current best narrow beam(generated on one panel) and the wide beam (generated on a secondpanel).

In one embodiment, the TRP only uses one of its panels, or,alternatively, the TRP is only equipped with one panel. In this case,the UE is triggered for transmission of two SRS resources, where the TRPuses a wide beam when receiving one of the SRS resources, and a narrowbeam when receiving the other SRS resource (other limitations of thisembodiment are as described above).

Accordingly, in one aspect there is provided a method for beammanagement. In one embodiment the method is performed by a network nodeand includes the network node using a first RX beam to receive a firstsignal (e.g., an SRS) transmitted by a user equipment, UE. The methodalso includes the network node obtaining, based on the first signalreceived using the first RX beam, a first received signal power value,P1 (e.g., an RSRP value). The method also includes the network nodeusing a second RX beam to receive the first signal or another signaltransmitted by the UE, wherein the first RX beam is wider than thesecond RX beam (in some embodiment the second RX beam is a previouslydetermined best beam). The method also includes the network nodeobtaining, based on the signal received using the second RX beam, asecond received signal power value, P2. The method also includes thenetwork node determining whether P2 exceeds P1 by at least a threshold.And the method also includes the network node determining whether toinitiate a beam sweep based on whether or not P2 exceeds P1 by at leastthe threshold.

In another aspect there is provided a network node that includesprocessing circuitry and a data storage system that store instructionsexecutable by said processing circuitry, whereby said network node isoperative to perform the above described method. In another aspect thereis provided a computer program comprising instructions which whenexecuted by processing circuitry causes the processing circuitry toperform any of the processes (methods) described herein. In oneembodiment there is a carrier containing this computer program, whereinthe carrier is one of an electronic signal, an optical signal, a radiosignal, and a computer readable storage medium.

An advantage of the embodiments is that they reduce overhead becausethey reduce the likelihood that the base station will unnecessarilyinitiate a U2 beam sweep. That is, by enabling the base station todetermine whether or not the currently selected narrow beam isperforming as well as a narrow beam should, the base station can make abetter decision about when to initiate a U2 beam sweep so that the basestation will avoid initiating a U2 sweep when the current narrow beam isperforming well enough.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated herein and form partof the specification, illustrate various embodiments.

FIGS. 1A, 1B, and 1C illustrate P1, P2, and P3 beam sweeps,respectively.

FIG. 2 illustrates two exemplary antenna panels, according to someembodiments.

FIGS. 3A and 3B illustrate U2 and U3 UL beam management procedures,respectively.

FIG. 4 illustrates an example data flow, according to an embodiment.

FIGS. 5A-5C illustrate example beam management procedures, according toan embodiment.

FIG. 6 illustrates example beam management procedures on a base stationwith two antenna panels, according to an embodiment.

FIG. 7A-7B illustrate example beam management procedures on a basestation with one antenna panel, according to an embodiment.

FIGS. 8A-8B illustrate example analysis for determining a thresholdvalue, according to an embodiment.

FIG. 9 is a flow chart illustrating a process according to someembodiments.

FIG. 10 is a block diagram illustrating a base station, according to anembodiment.

DETAILED DESCRIPTION

FIG. 4 is a message flow diagram illustrating one embodiment of thisdisclosure. In this embodiment, a base station 402 is serving a UE 404.UE 404 may be any device capable of wireless communicating with basestation 402. For example, UE 404 may be a mobile phone, a tablet, alaptop, a sensor (or other internet of things (IoT) device), or anyother device with wireless communication capabilities. Base station 402may be any network entity that is capable of wirelessly communicatingwith UEs and providing network access to the UEs. For example, in oneembodiment base station 102 is a 5G base station (gNB).

Base station 402, in this example, configures UE 404 with: i) a firstSRS set with usage ‘beamManagment’ with a single SRS resource and iii) asecond SRS resource set with usage ‘beamManagment’ with a single SRSresource and with a repetition factor=N. The repetition factor of Nallows base station 402 to sweep through N TRP beams per TRP panel (insome embodiments N=4, in other embodiments N=12, in yet other embodimentN is any number greater than 1). If base station 402 decides to evaluatemore than N TRP beams per TRP panel, base station 402 can trigger thetransmission of the SRS set multiple times, and/or base station 402 canhave multiple SRS resource sets that are triggered after each other. Forexample, as shown in FIG. 4 , base station 402 transmits to UE 404 amessage m402 that includes an SRS-Config IE which includes the first andsecond SRS resource sets.

Base station 402 then transmits to UE 404 a trigger message m404 (e.g.,a DCI that contains an aperiodic SRS-ResourceTrigger or a MAC controlelement (CE)) that identifies (directly or indirectly) the first SRSresource set and triggers UE 404 to use a UE TX beam 502 (see FIG. 5A)to transmit an SRS m406 in accordance with the SRS resource included inthe identified SRS resource set. As shown in FIG. 5A, base station 402receives the SRS m406 at a first antenna panel 591 using a wide beam 506and receives the SRS m406 at a second antenna panel 592 using a narrowbeam 508. The wide beam 506 can be either the best SSB beam for that UE404 or a cell-covering beam, and the narrow beam 508 can be a previouslydetermined best narrow beam (e.g., a narrow beam selected as a result ofperforming a beam sweep such as a U2 beam sweep). Using the best SSBbeam as the wide beam 506 can evaluate if UE 404 if there is a betternarrow beam within beam 506. Using a cell-covering beam (e.g., anelement pattern) can determine if there are any narrow TRP beams in anydirection within the coverage of the element pattern that is better thanbeam 506.

After receiving the SRS using the wide beam 506 and the narrow beam 508,base station 402 determines whether to initiate a U2 beam sweep (seestep s407). For example, base station 402 determines whether to initiatea UE beam sweep based on a difference between (1) the RSRP of thereceived SRS for narrow beam 508 and (2) the RSRP of the received SRSfor wide beam 506. More specifically, in this embodiment, as shown inFIG. 5B, base station 402 compares the RSRP of the received SRS for thewide beam 506 (denoted “RSRPw”) and the RSRP of the received SRS for thenarrow beam 508 (denoted “RSRPn”) and determines whether a difference513 between RSRPn and RSRPw is less than a threshold amount 514. IfRSRPn-RSRPw is less than the threshold amount 514, then there is a riskthat there exists a narrow beam that would perform better than narrowbeam 508 because the threshold 514 is chosen such that it is generallyexpected that the best narrow beam should outperform the wide beam by atleast the threshold 514. Accordingly, base station 402 can decide basedon the RSRP measurements whether or not to trigger the SRS resource setwith a repetition factor of four to evaluate different candidate TRPbeams (i.e., initiate the U2 beam sweep).

If base station 402 determines to initiate the U2 beam sweep, basestation 402 sends to UE 404 a trigger message m408 that identifies(directly or indirectly) the second SRS resource set and that triggersUE 404 to transmit an SRS at four different times 411, 412, 413, and414, as shown in FIG. 4 . Base station 402 then, based on measurementsof the SRS transmission, selects a TRP RX beam 417.

For example, as shown in FIG. 5C, base station 402 sweeps through a setof four TRP RX beams 524-528 such that each one of the beams is used toreceive one of the four SRS transmissions triggered by trigger messagem408 (as shown in FIG. 5C, UE 404 uses UE TX beam 522 to perform the SRStransmissions). Base station 402 performs an RSRP measurement for eachone of the TRP RX beams to identify the TRP RX beam that produces thehighest RSRP measurement.

In another embodiment, instead of base station 402 applying thediscussed process during a single SRS resource transmission, basestation 402 performs the process during a U3 beam sweep. This isillustrated in FIG. 6 .

In the example illustrated in FIG. 6 , UE 404 first transmits the SRSusing beam 602, then transmits the SRS using beam 604, and thentransmits the SRS using beam 606. For each one of these three SRStransmission, base station 402 simultaneously receives the transmissionusing wide beam 506 and narrow beam 508, and, for each beam, determinesthe RSRP for the SRS transmission. Thus, base station 402 will producethe following three pairs of RSRP measurements: (RSRPw1,RSRPn1),(RSRPw2,RSRPn2), and (RSRPw3,RSRPn3), where RSRPw1 and RSRPn1 aredetermined based on the first SRS transmission, RSRPw2 and RSRPn2 aredetermined based on the second SRS transmission, and RSRPw3 and RSRPn3are determined based on the third SRS transmission. Base station 402then compares RSRPn1, RSRPn2, and RSRPn3 to determine which is thegreatest. If we assume RSRPn1 is greater than RSRPn2 and RSRPn3, thenbase station 402 computes diff=RSRPn1−RSRPw1. If diff is less than thethreshold 514, then base station 402 will initiate the U2 beam sweep.

In another exemplary embodiment, base station 402 uses received datainstead of a received SRS to determine the difference in received powerbetween the current best narrow beam (generated on one panel) and thewide beam (generated on a second panel).

FIGS. 7A and 7B illustrate an embodiment where base station 402 onlyuses one TRP panel 791 when receiving the SRSs. For example, basestation 402 is equipped with only one panel, or base station 402 wantsto use the other TRP panels for other tasks. In this embodiment, UE 404is configured with an SRS resource set with two SRS resources.Alternatively, UE 404 may be configured with an SRS resource set with asingle SRS resource having a repetition factor of 2. In either case, asa result of receiving one or more trigger messages transmitted by basestation 402 to UE 404, UE 404 transmits, at a first point in time, anSRS and then transmits an SRS at a later, second point in time. Thefirst SRS transmission by UE 404 is received by base station 402 usingwide beam 506 (see FIG. 7A), and the second SRS transmission by UE 404is received by base station 402 using narrow beam 508 (see FIG. 7B). Aswith the first embodiment, base station 402 then computesdiff=RSRPn−RSRPw, where RSPRn is the RSRP of the received SRS for thenarrow beam 508, and RSPRw is the RSRP of the received SRS for the widebeam 506. Then, based on whether diff is less than the threshold 514,base station 402 determines whether or not to initiate the U2 sweep.

Determining the Threshold

The threshold can be determined in several different ways. A few,non-limiting examples are described below.

In one example, where UE 404 is in a line-of-sight (LOS) scenariowithout any angular spread, the narrow beam should have an RSRP that isapproximately 10*log 10(numberAntennaElemntsInPanel) larger than theRSRP of the wide beam (assuming base station 402 applies the elementpattern of the wide beam and that UE 404 is located in the samedirection as the highest gain of the narrow beam). If base station 402uses untapered DFT beam without oversampling, there is, roughly, a 4 dBgain drop at the cross over between adjacent beams. So in this example,the threshold corresponds to 10*log 10(numberAntennaElemntsInPanel)−4dB. If the wide beam has less received power than the narrow beam minusthe threshold, there is a substantial chance that there exists a betternarrow beam, and base station 402 can accordingly initiate a beam sweep.

In another example, where there is angular spread at base station 402,the RSRP gains for the narrow beam will be more difficult to predict.FIGS. 8A and 8B show simulations using channel matrices extracted from adynamic simulator (for UMi scenario). FIGS. 8A and 8B indicate that, fora TRP panel with 4×8 elements, the best narrow beam is at least 5 dBbetter than the wide beam in almost 100% of all cases. Accordingly, ifthe threshold is 5 dB and the RSRP of the wide TRP beam+the threshold islarger than the RSPR for the narrow TRP beam, there is a large chancethat the narrow TRP is not the best one. Base station 402 can theninitiate a U2 beam sweep.

However, the threshold does not need to require an approximately 100%certainty that the narrow beam is not the best. In most situations,there is a large risk that base station 402 is using a sub-optimalnarrow TRP beam. The threshold value can balance the overhead requiredfrom beam management with an importance of using the best narrow beam.In one embodiment, if the system has a high sensitivity to extraoverhead signaling, the threshold is smaller. In another embodiment, ifUE 404 has a highly sensitive link budget which corresponds to a highimportance for using the best narrow TRP beam, the threshold is larger.

In some examples, the threshold is adjusted adaptively to maximizeperformance. If the threshold is too small, there may be manytransmissions with suboptimal TRP RX beam leading to poor performance.The threshold can then be increased as long as performance increases andthe overhead does not become too large. In some examples, machinelearning can be used to find the optimal threshold.

Therefore, as indicated above, for UL beam management (or other ULtransmissions), the present disclosure provides for using a wide RX beamon one TRP panel of base station 402 and the current best narrow TRPbeam on the second panel of base station 402. If the RSRP from thenarrow beam minus the received power of the wide beam is smaller than acertain threshold, base station 402 triggers a more advanced UL beammanagement procedure (i.e., U2), in order to update the TRP beam for UE404. The threshold is determined based on how sensitive the system isfor overhead signaling and how sensitive the link budget is for UE 404.

FIG. 9 is a flowchart illustrating a beam management process 900,according to an embodiment, that is performed by a network node (e.g.,base station 404). Process 900 may begin in step s902.

Step s902 comprises the network node using a first RX beam to receive afirst signal transmitted by a UE (e.g., UE 404). For example, the firstRX beam is wide beam 506 as illustrated in FIG. 5A. For example, thefirst signal is SRS m406, as discussed with respect to FIG. 4 .

Step s904 comprises the network node obtaining, based on the firstsignal received using the first RX beam, a first received signal powervalue, P1. For example, P1 is RSRPw as discussed with respect to FIG.5B.

Step s906 comprises the network node using a second RX beam to receivethe first signal or another signal transmitted by the UE, wherein thefirst RX beam is wider than the second RX beam. For example, the secondRX beam is narrow beam 508 as illustrated in FIG. 5B.

Step s908 comprises the network node obtaining, based on the signalreceived using the second RX beam, a second received signal power value,P2. For example, P2 is RSRPn as discussed with respect to FIG. 5B.

Step s910 comprises determining whether P2 exceeds P1 by at least athreshold. For example, step s910 is performed according to any of themethods of determining the threshold, as discussed above.

Step s912 comprises determining whether to initiate a beam sweep basedon whether or not P2 exceeds P1 by at least the threshold. For example,step s912 corresponds to the base station 402 determines whether toinitiate a U2 beam sweep 407, as discussed regarding FIG. 4 .

In some examples, the process 900 further includes, as a result ofdetermining that P2 does not exceed P1 by at least the threshold, thenetwork node initiating the beam sweep. In some examples, initiating thebeam sweep comprises the network node transmitting to the UE a triggermessage that is associated with a beam management Sounding ReferenceSignal, SRS, resource set that identifies an SRS resource and thattriggers the UE to transmit a plurality of reference signals inaccordance with the SRS resources set.

In some examples, process 900 further includes, for each RX beamincluded in a set of RX beams, using the RX beam to receive one of theplurality of reference signals and determining a reference signalreceived power (RSRP) value for the reference signal received using theRX beam, and selecting an RX beam from the set of RX beams based on thedetermined RSRP values.

In some examples, the first signal is a first reference signal. In someexamples, process 900 includes, prior to receiving the first referencesignal, transmitting to the UE a first trigger message that triggers theUE to transmit the first reference signal. For example, the triggermessage is trigger message m404 as discussed with respect to FIG. 4 .For example, the first trigger message that triggers the UE to transmitthe first reference signal is associated with a beam management SRSresource set that identifies a single SRS resource.

In some examples of process 900, the network node uses the second RXbeam to receive said other signal and said other signal is a secondreference signal. In some examples, the method further comprises, priorto receiving the second reference signal, transmitting to the UE asecond trigger message that triggers the UE to transmit the secondreference signal. For example, the second trigger message is triggermessage m408 as discussed with respect to FIG. 4 .

In some examples, the second trigger message that triggers the UE totransmit the second reference signal is associated with the beammanagement SRS resource set that identifies the single SRS resource.

In some examples of process 900, the network node comprises a firstantenna panel and a second antenna panel. For example, the first antennapanel is panel 591 of FIG. 5A, and the second antenna panel is panel 592of FIG. 5A. In this embodiment, using the first RX beam to receive thefirst signal comprises using the first antenna panel, but not the secondantenna panel, to receive the first signal, and using the second RX beamto receive the first signal or the another signal comprises using thesecond antenna panel, but not the first antenna panel, to receive thefirst signal.

In some examples, process 900 further includes i) using the first RXbeam to receive a second signal transmitted by the UE; ii) obtaining,based on the second signal received using the first RX beam, a thirdreceived signal power value, P3; iii) using the second RX beam toreceive the second signal transmitted by the UE; iv) obtaining, based onthe second signal received using the second RX beam, a fourth receivedsignal power value, P4; and v) determining that P2 is greater than P4.In some examples, the step of determining whether to initiate the beamsweep based on whether or not P2 exceeds P1 by at least the threshold isperformed as a result of determining that P2 is greater than P4.

In some examples of process 900, the threshold is based on a link budgetsensitivity and/or a current load of the network node.

In some examples of process 900, the threshold is at least 5 dB.

FIG. 10 is a block diagram of the network node 1000 (e.g., base station402), according to some embodiments. As shown in FIG. 10 , network node1000 may comprise: processing circuitry (PC) 1002, which may include oneor more processors (P) 1055 (e.g., one or more general purposemicroprocessors and/or one or more other processors, such as anapplication specific integrated circuit (ASIC), field-programmable gatearrays (FPGAs), and the like), which processors may be co-located in asingle housing or in a single data center or may be geographicallydistributed (i.e., network node 1000 may be a distributed computingapparatus); a network interface 1068 comprising a transmitter (Tx) 1065and a receiver (Rx) 1067 for enabling network node 1000 to transmit datato and receive data from other network nodes connected to a network 1010(e.g., an Internet Protocol (IP) network) to which network interface4048 is connected; communication circuitry 4048, which is coupled to anantenna arrangement 4049 comprising one or more antennas and whichcomprises a transmitter (Tx) 4045 and a receiver (Rx) 4047 for enablingthe network node to transmit data and receive data (e.g., wirelesslytransmit/receive data); and a local storage unit (a.k.a., “data storagesystem”) 1008, which may include one or more non-volatile storagedevices and/or one or more volatile storage devices. In embodimentswhere PC 1002 includes a programmable processor, a computer programproduct (CPP) 4041 may be provided. CPP 4041 includes a computerreadable medium (CRM) 4042 storing a computer program (CP) 4043comprising computer readable instructions (CRI) 4044. CRM 4042 may be anon-transitory computer readable medium, such as, magnetic media (e.g.,a hard disk), optical media, memory devices (e.g., random access memory,flash memory), and the like. In some embodiments, the CRI 4044 ofcomputer program 4043 is configured such that when executed by PC 1002,the CRI causes the network node to perform steps described herein (e.g.,steps described herein with reference to the flow charts). In otherembodiments, the network node may be configured to perform stepsdescribed herein without the need for code. That is, for example, PC1002 may consist merely of one or more ASICs. Hence, the features of theembodiments described herein may be implemented in hardware and/orsoftware.

While various embodiments are described herein, it should be understoodthat they have been presented by way of example only, and notlimitation. Thus, the breadth and scope of this disclosure should not belimited by any of the above-described exemplary embodiments. Moreover,any combination of the above-described elements in all possiblevariations thereof is encompassed by the disclosure unless otherwiseindicated herein or otherwise clearly contradicted by context.

Additionally, while the processes described above and illustrated in thedrawings are shown as a sequence of steps, this was done solely for thesake of illustration. Accordingly, it is contemplated that some stepsmay be added, some steps may be omitted, the order of the steps may bere-arranged, and some steps may be performed in parallel.

1. A method for beam management, the method being performed by a networknode, the method comprising: using a first receive (RX) beam to receivea first signal transmitted by a user equipment (UE); obtaining, based onthe first signal received using the first RX beam, a first receivedsignal power value, P1; using a second RX beam to receive the firstsignal or another signal transmitted by the UE, wherein the first RXbeam is wider than the second RX beam; obtaining, based on the signalreceived using the second RX beam, a second received signal power value,P2; determining whether P2 exceeds P1 by at least a threshold; anddetermining whether to initiate a beam sweep based on whether or not P2exceeds P1 by at least the threshold.
 2. The method of claim 1, furthercomprising: as a result of determining that P2 does not exceed P1 by atleast the threshold, initiating the beam sweep.
 3. The method of claim2, wherein initiating the beam sweep comprises transmitting to the UE atrigger message that is associated with a beam management SoundingReference Signal (SRS) resource set that identifies an SRS resource andthat triggers the UE to transmit a plurality of reference signals inaccordance with the SRS resources set.
 4. The method of claim 3, furthercomprising: for each RX beam included in a set of RX beams, using the RXbeam to receive one of the plurality of reference signals anddetermining a reference signal received power (RSRP) value for thereference signal received using the RX beam; and selecting an RX beamfrom the set of RX beams based on the determined RSRP values.
 5. Themethod of claim 1, wherein the first signal is a first reference signal,and the method further comprises, prior to receiving the first referencesignal, transmitting to the UE a first trigger message that triggers theUE to transmit the first reference signal.
 6. The method of claim 5,wherein the first trigger message that triggers the UE to transmit thefirst reference signal is associated with a beam management SRS resourceset that identifies a single SRS resource.
 7. The method of claim 5,wherein the network node uses the second RX beam to receive said othersignal; said other signal is a second reference signal, and the methodfurther comprises, prior to receiving the second reference signal,transmitting to the UE a second trigger message that triggers the UE totransmit the second reference signal.
 8. The method of claim 7, whereinthe second trigger message that triggers the UE to transmit the secondreference signal is associated with the beam management SRS resource setthat identifies the single SRS resource.
 9. The method of claim 1,wherein the network node comprises a first antenna panel and a secondantenna panel, using the first RX beam to receive the first signalcomprises using the first antenna panel, but not the second antennapanel, to receive the first signal, and using the second RX beam toreceive the first signal or the another signal comprises using thesecond antenna panel, but not the first antenna panel, to receive thefirst signal.
 10. The method of claim 1, further comprising: using thefirst RX beam to receive a second signal transmitted by the UE;obtaining, based on the second signal received using the first RX beam,a third received signal power value, P3; using the second RX beam toreceive the second signal transmitted by the UE; obtaining, based on thesecond signal received using the second RX beam, a fourth receivedsignal power value, P4; and determining that P2 is greater than P4,wherein the step of determining whether to initiate the beam sweep basedon whether or not P2 exceeds P1 by at least the threshold is performedas a result of determining that P2 is greater than P4.
 11. The method ofclaim 1, wherein the threshold is based on a link budget sensitivityand/or a current load of the network node.
 12. The method of claim 1,wherein the threshold is at least 5 dB.
 13. A non-transitory computerreadable storage medium storing a computer program comprisinginstructions which when executed by processing circuitry causes theprocessing circuitry to perform the method of claim
 1. 14-15. (canceled)16. A network node, comprising: processing circuitry; and a data storagesystem, said data storage system storing instructions executable by saidprocessing circuitry, wherein said network node is configured to performa method comprising: using a first receive (RX) beam to receive a firstsignal transmitted by a user equipment (UE); obtaining, based on thefirst signal received using the first RX beam, a first received signalpower value, P1; using a second RX beam to receive the first signal oranother signal transmitted by the UE, wherein the first RX beam is widerthan the second RX beam; obtaining, based on the signal received usingthe second RX beam, a second received signal power value, P2;determining whether P2 exceeds P1 by at least a threshold; anddetermining whether to initiate a beam sweep based on whether or not P2exceeds P1 by at least the threshold.
 17. The network node of claim 16,wherein the method further comprises: as a result of determining that P2does not exceed P1 by at least the threshold, initiating the beam sweep.18. The network node of claim 17, wherein initiating the beam sweepcomprises transmitting to the UE a trigger message that is associatedwith a beam management Sounding Reference Signal (SRS) resource set thatidentifies an SRS resource and that triggers the UE to transmit aplurality of reference signals in accordance with the SRS resources set.19. The network node of claim 18, wherein the method further comprises:for each RX beam included in a set of RX beams, using the RX beam toreceive one of the plurality of reference signals and determining areference signal received power (RSRP) value for the reference signalreceived using the RX beam; and selecting an RX beam from the set of RXbeams based on the determined RSRP values.
 20. The network node of claim16, wherein the first signal is a first reference signal, and the methodfurther comprises, prior to receiving the first reference signal,transmitting to the UE a first trigger message that triggers the UE totransmit the first reference signal.
 21. The network node of claim 20,wherein the first trigger message that triggers the UE to transmit thefirst reference signal is associated with a beam management SRS resourceset that identifies a single SRS resource.
 22. The network node of claim20, wherein the network node uses the second RX beam to receive saidother signal; said other signal is a second reference signal, and themethod further comprises, prior to receiving the second referencesignal, transmitting to the UE a second trigger message that triggersthe UE to transmit the second reference signal.